At least three people dead and many more injured after Amtrak train derails in Montana

People work at the scene of an Amtrak train derailment in north-central Montana - Kimberly Fossen via AP

At least three people died on Saturday and some passengers were injured after seven cars of an Amtrak train went off the rails in north-central Montana, an official at a local sheriff's office said.

The National Transportation Safety Board said late on Saturday it will investigate the incident.

People trapped aboard soon after the derailment have all been taken off the train, said the official of the Liberty County Sheriff's Office, who spoke on condition of anonymity.

There were multiple injuries but no final count, the official added. A social media user posted photos of train cars on their side after the incident and other damaged train cars.

An ambulance parked at the scene of the derailment - Kimberly Fossen via AP

The cause of the incident was not immediately clear.

The Seattle-bound Empire Builder train had about 146 passengers and 16 crew aboard when seven cars derailed near Joplin, Amtrak said.

The 10-car train with two locomotives had departed from Chicago.

Megan Vandervest, a passenger on the train who was going to visit a friend in Seattle, told The New York Times that she was awakened by the derailment.

"My first thought was that we were derailing because, to be honest, I have anxiety and I had heard stories about trains derailing," said Ms Vandervest, who is from Minneapolis. "My second thought was that's crazy. We wouldn't be derailing. Like, that doesn't happen."

She told the New York Times that the car behind hers was tilted over, the one behind that was entirely tipped over, and the three cars behind that "had completely fallen off the tracks and were detached from the train".

Speaking from the Liberty County Senior Center, where passengers were being taken, Ms Vandervest said it felt like "extreme turbulence on a plane."

Amtrak said Empire Builder trains originating on Saturday are cancelled between Minot, North Dakota and Shelby, Montana, while on Sunday the westbound Empire Builder train will terminate in Minneapolis and an eastbound Empire Builder train will originate in Minneapolis.